Conventionally, in a liquid discharge apparatus, for example, an ink jet head disclosed in Japanese Patent Application Laid-Open No. 2002-59547, a piezoelectric actuator is disposed as opposed to a pressure chamber of a cavity unit and capacity of the pressure chamber is changed by displacement of the piezoelectric actuator, thereby discharging ink.
FIG. 1 schematically shows an ink jet head 910. In a piezoelectric actuator 921, a plurality of ceramic layers 962 are stacked with individual electrodes 952 and common electrodes 953 interposed alternately, and a region of the ceramic layer 962 sandwiched between the individual electrode 952 and the common electrode 953 in the vertical direction is an activated part. By grounding the common electrode 953 and selectively applying voltage to the individual electrode 952, the corresponding activated part is displaced, thereby applying discharge pressure to liquid in a pressure chamber 924.
Since the piezoelectric actuator 921 is generally formed by laminating green sheets made of ceramics such as PZT and sintering them, a minute defect (crack) 960 is easy to occur in the ceramic layer 962 as a sintered body. When, in a lowermost ceramic layer 962a which covers an opening of the pressure chamber 924, the defect 960 extends from the surface of the pressure chamber 924 to the electrode as shown in FIG. 1, disadvantageously, ink penetrates into the lowermost ceramic layer 962a from the pressure chamber 924 through the defect 960, causing electrical short circuit between the electrodes.
Thus, in Japanese Patent Application Laid-Open No. 2002-59547, an ink impermeable adhesive sheet is used to adhere a cavity unit 920 to the piezoelectric actuator 921 and the adhesive sheet covers the whole surface of the piezoelectric actuator 921 opposed to the cavity unit 920. Thus, the ceramic layers 962 of the piezoelectric actuator 921 do not directly contact ink.